1. Field of the Invention
The present invention relates to a centrifugal compressor, and more particularly to a centrifugal compressor having an abradable layer embedded in a compressor casing inner wall and cut by a rotating impeller.
2. Description of the Related Art
Various centrifugal compressors are known in the art. One type of centrifugal compressor includes a casing, an impeller housed in the casing, and an abradable layer provided on an inner surface of the casing such that it is cut by the impeller rotating in the casing. As the compressor is activated and the impeller rotates, the clearance between the impeller and the abradable layer is eventually adjusted to an optimum value. This type of centrifugal compressor improves an operation efficiency. Such centrifugal compressor is disclosed in, for example, Japanese Patent Application, Laid-Open Publication No. 6-257454 published on Sep. 13, 1994.
Referring to FIG. 6 of the accompanying drawings, illustrated is another conventional centrifugal compressor. This is a multi-stage centrifugal compressor 61 including a casing 64 and two impellers 62 and 63 mounted on ends of a common rotating shaft 65. If the teaching of Japanese Patent Application, Laid-Open Publication No. 6-257454 is applied to the illustrated centrifugal compressor 61, two abradable layers (not shown) will be embedded in the casing inner walls 66 and 67 in the vicinity of both the impellers 62 and 63 respectively.
However, the abradable layer is expensive so that providing the abradable layers for the two impellers 62 and 63 will raise a manufacturing cost of the compressor 61.
Incidentally, the abradable layer taught in Japanese Patent Application, Laid-Open Publication No. 6-257454 also extends along the impeller 62, 63 from its front edge 72 to rear edge 79.